Valve mechanism with a variable valve opening cross-section

ABSTRACT

The invention relates to a valve mechanism with a variable valve opening cross section, in which the valve mechanism is disposed at an admission opening of an internal combustion engine and has a gas exchange valve, which is acted on by the force of a valve spring and is displaceable axially back and forth inside a guide by a valve control unit; the position of the sealing slide relative to the gas exchange valve in the axial direction is continuously variable by means of an adjusting unit.  
     It is provided that a sealing slide ( 10 ) is disposed coaxially to the gas exchange valve ( 12 ), is acted upon by the force of a coupling spring ( 24 ), and is displaceable axially back and forth by the valve control unit. The position of the sealing slide ( 10 ) is variable in the axial direction relative to the gas exchange valve ( 12 ) by means of an adjusting unit.

[0001] The invention relates to a valve mechanism with a variable valveopening cross section having the characteristics recited in the preambleto claim 1.

PRIOR ART

[0002] It is known to use internal combustion engines as driving enginefor motor vehicles. In them, a fuel-air mixture is compressed andignited in the work chamber. The energy produced is converted intomechanical work. It is known for air or the fuel-air mixture to bedelivered to the work chamber via valves (inlet valves), and for theproducts of combustion to be removed from the work chamber via valves(outlet valves). For determining the efficiency of the engine,controlling these valves is of great significance. In particular, thegas exchange in the work chamber is controlled by way of controlling thevalves.

[0003] In addition to camshaft control, it is also known to employ anelectrohydraulic valve control. Electrohydraulic valve control offersthe capability of variable or fully variable valve control, making itpossible to optimize the gas exchange and thus to enhance the motorefficiency of the engine.

[0004] The electrohydraulic valve control includes a hydraulicallyactuatable control valve, whose control valve piston actuates a valvebody of the inlet and outlet valves and leads to a valve seat (valveseat ring) (closure of the valve) or moves away from it (opening of thevalve). The control valve can be actuated via a pressure control of ahydraulic medium. The pressure control is effected here via magnetvalves incorporated into the hydraulic circuit. To achieve the mostoptimal possible gas exchanges, the highest possible switching speeds ofthe control valve are needed. As a result of these high switchingspeeds, the valve body of the inlet and outlet valves strikes the valveseat ring at high speed. The result is on the one hand noise, and on theother, the partners in the valve suffer relatively high wear.

[0005] European Patent Disclosure EP 0 455 761 B1, for instance, has ahydraulic valve control device for an internal combustion engine as itssubject. The fundamental technological principle of this embodiment isto displace a motor valve by means of a controlled pressure of ahydraulic fluid. In this embodiment, it is provided that an electroniccontrol unit triggers a magnet valve, which in turn controls the motionof a storage piston, by way of which the stroke of the motor valve isvaried.

[0006] European Patent Disclosure EP 0 512 698 A1 describes anadjustable valve system for an internal combustion engine. Thisembodiment is one example of mechanical valve control via cams of arotating camshaft.

[0007] U.S. Pat. No. 4,777,915 has an electromagnetic valve controlsystem for an internal combustion engine as its subject. A similarembodiment of an electromagnetic valve control is known from EP 0 471614 A1. In these embodiments, the valve is moved back and forth todifferent positions by electromagnetic force. The electromagnets aredisposed inside a housing part of the cylinder head, in two differentregions. By the alternating activation of the electromagnets, the valveis moved alternatingly into two terminal positions, corresponding to theopening and closing positions of the valve, respectively. In theseterminal positions of the valve, the admission opening to the combustionchamber of the fuel-air mixture is then opened to the widest extent orcompletely closed.

[0008] Another embodiment is known from EP 0 551 271 B1. This embodimentinvolves a valve mechanism with a plate valve, which is disposed in apassage of an internal combustion engine. The fundamental principle ofthis embodiment is that the valve plate is divided in two; one half ofthe valve plate executes only a fraction of the stroke executed by theother half of the valve plate.

[0009] In these known embodiments for valve control, the major effort ofproduction and assembly of the valve mechanism, because of itscomplicated design, is especially disadvantageous. This adverselyaffects the costs for production and assembly. Moreover, in theseembodiments, extremely high speeds and strong forces for valve controlare necessary, so that an increased vulnerability to malfunction of thevalve control from major wear of the parts of the valve mechanism isunavoidable.

ADVANTAGES OF THE INVENTION

[0010] The valve mechanism of the invention having the definitivecharacteristics of the main claim offers the advantage over the priorart of creating a variable valve opening cross section by simple means.Because a sealing slide is disposed coaxially to the gas exchange valve,is acted upon by the force of a coupling spring, and is displaceableaxially back and forth by the valve control unit, and because theposition of the sealing slide relative to the gas exchange valve in theaxial direction is variable by an adjusting unit, which essentiallycomprises a control slide that is adjustable in the axial direction ofthe gas exchange valve and is disposed coaxially to the gas exchangevalve and to the sealing slide, a valve mechanism is created which has asimple design and which functions reliably and durably. The advantage ofthe valve mechanism of the invention is in particular that a variablevalve opening cross section can be created, and each individual valvecan be regulated separately. With the valve mechanism of the invention,the variable valve opening cross section can advantageously be createdwithout high speeds and without strong forces, so that the vulnerabilityof this valve mechanism to malfunction is very slight. The valvemechanism of the invention can be produced and assembled economically,because of its simple design. The invention advantageously creates avariable valve control by which optimization of the gas exchange andthus an increase in motor efficiency of the engine is possible.

[0011] In a preferred feature of the invention, it is provided that thevalve control unit is a camshaft.

[0012] In a further preferred feature of the invention, it is providedthat the gas exchange valve has a rotationally symmetrical basicconstruction and comprises a valve shaft, on whose lower end a valveplate is disposed.

[0013] In a further preferred feature of the invention, it is providedthat the valve plate has a conical circumferential face, which forms thesealing seat of the gas exchange valve.

[0014] Also in a preferred feature of the invention, it is provided thatin the closing position of the valve mechanism, the sealing seat of thegas exchange valve directly contacts both a sealing seat of the sealingslide and a valve seat ring of the cylinder head.

[0015] Moreover, in a preferred feature of the invention, it is providedthat the sealing slide comprises a bushlike bearing body, which isdisposed displaceably axially back and forth inside a guide of thecylinder head.

[0016] As a result of these advantageous features of the invention, thedelivery of the air, or the fuel-air mixture, can be regulated withgreat precision, and a high efficiency of the engine can thus beachieved.

[0017] Moreover, in a preferred feature of the invention, it is providedthat the control slide is connected via a male thread to a correspondingfemale thread of a gear wheel, surrounding it, that is connected to arack by which a longitudinal motion can be executed. The particularadvantage of this preferred feature of the invention is that with it, avery economical embodiment is created, which advantageously makes itpossible for all the inlet and/or outlet valves of an internalcombustion engine to be regulated in common via a single component.Triggering a plurality of control slides via this component creates theprecondition that allows the control system of the engine to work withonly a single sensor.

[0018] Moreover, in a preferred feature of the invention, it is providedthat associated with the control slide is a securing disk, by way ofwhich the control slide is adjustable in the axial direction. As aresult, it is advantageously possible to calibrate the positions of thecontrol slide of an internal combustion engine exactly by compensatingfor existing tolerances. The individual work cylinders of an engine canbe adapted precisely to one another in their function in this simple andadvantageous way, and thus an optimal efficiency of the engine can beachieved.

[0019] Further advantageous features of the invention will becomeapparent from the characteristics recited in the dependent claims.

DRAWINGS

[0020] The invention will be described below in further detail in termsof exemplary embodiments in conjunction with the associated drawings.Shown are:

[0021]FIG. 1, a side view of the valve mechanism of the invention, witha camshaft;

[0022]FIG. 2, a plan view on the valve mechanism of the invention andthe camshaft of FIG. 1;

[0023]FIG. 3, a section taken along the line A-A in FIG. 2 through acylinder head with the valve mechanism of the invention and with acamshaft, involving a first exemplary embodiment of the invention;

[0024]FIG. 4, a detail X of FIG. 3;

[0025]FIG. 5, a section taken along the line B-B in FIG. 2 through acylinder head with the valve mechanism of the invention and without thecamshaft, involving a first exemplary embodiment of the invention;

[0026]FIG. 6, a section taken along the line C-C of FIG. 5;

[0027]FIG. 7, a section taken along the line D-D of FIG. 5;

[0028]FIG. 8, a detail Y of FIG. 5;

[0029]FIG. 9, a perspective view of a control slide of the valvemechanism of the invention in a first exemplary embodiment of theinvention;

[0030]FIG. 10, a section taken along the line A-A in FIG. 2 through acylinder head with the valve mechanism of the invention and with acamshaft, involving a second exemplary embodiment of the invention;

[0031]FIG. 11, a detail X of FIG. 10;

[0032]FIG. 12, a section taken along the line B-B in FIG. 1 through acylinder head with the valve mechanism of the invention and without thecamshaft, involving a second exemplary embodiment of the invention;

[0033]FIG. 13, a section taken along the line C-C of FIG. 12;

[0034]FIG. 14, a perspective view of a control slide of the valvemechanism of the invention in a second exemplary embodiment of theinvention; and

[0035]FIG. 15, a perspective view of a sealing slide of the valvemechanism of the invention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENT

[0036] In the fifteen drawing figures, the individual parts of the valvemechanism of the invention are shown schematically and only with thosecomponents essential to the invention. Identical parts of the valvemechanism of the invention are identified by the same reference numeralsthroughout the drawings and as a rule will each be described only once.

[0037] In FIGS. 1 and 2, the valve mechanism of the invention, with acamshaft 44 as the valve control unit, is shown in a side view and aplan view, respectively, in its disposition on the cylinder head 18 ofan internal combustion engine. In FIG. 2, two cams are disposed on thecamshaft 44, by each of which the axial displacement motion of one gasexchange valve 12 is controlled.

[0038]FIG. 3 shows the valve mechanism of the invention with itsessential components in a sectional view of a first exemplary embodimentof the invention. The valve mechanism has a gas exchange valve 12, whichis acted upon by the force of a valve spring 16. The gas exchange valve12 is displaceable axially back and forth inside a guide, and thedisplacement motion is generated by a valve control unit. In a preferredfeature of the invention, a camshaft 44 is provided as the valve controlunit.

[0039] The gas exchange valve 12 has a rotationally symmetrical basicconstruction and comprises a valve shaft 14, on the lower end of which avalve plate 20 is disposed. FIG. 3 shows the valve mechanism in theclosing position of the gas exchange valve 12. The sealing seat 28 ofthe gas exchange valve 12 is in direct contact with both a sealing seat30 of the sealing slide 10 and a valve seat ring 22 of the cylinder head18.

[0040] The structure and mode of operation of gas exchange valves 12 perse are well known, so that this need not be addressed in further detailin the context of the present description.

[0041] The invention provides that a sealing slide 10 is disposedcoaxially to the gas exchange valve 12. The sealing slide 10 is actedupon by the force of a coupling spring 24 and is displaceable axiallyback and forth. The displacement motion of the sealing slide 10 islikewise generated by the camshaft 40, by which the displacement motionof the gas exchange valve 12 is controlled.

[0042] In FIG. 15, the sealing slide 10 is shown schematically in aperspective view. The sealing slide 10 substantially comprises a bearingbody 40 and a sealing body 38. The bearing body 40 of the sealing slide10 is embodied in bushlike fashion and is disposed displaceably axiallyback and forth inside a guide of the cylinder head 18. On its lower end,the sealing slide 10 has a cylindrical sealing body 38, whose outer faceforms the sealing seat 30, and whose outer wall, together with the valveseat ring 22, forms an annular gap seal. The sealing body 38 isconnected to the bearing body 40 via connecting rods 42.

[0043] A stop disk 26 is secured to the bearing body 40, near the lowerend thereof. To facilitate assembly, this stop disk 26 comprises twoparts. The two parts of the stop disk 26 are surrounded by a clampingring 36, by which they are held together.

[0044] The connection between the sealing body 38 and the bearing body40 is designed such that sufficient room remains for the air flowingthrough, or for the fuel-air mixture. As a result, for letting the airor the fuel-air mixture both in and out, there is advantageously a largeenough admission opening inside the sealing slide 10 to allow thismedium to flow through unhindered.

[0045]FIG. 8 shows a detail Y of FIG. 5. In this view, it can readily beseen that a control slide 34 is disposed coaxially to both the gasexchange valve 12 and the sealing slide 10. The control slide 34 (FIG.9) is provided with a male thread 46, by way of which it is connected toa corresponding female thread 48 of a gear wheel 50 surrounding it. Asecuring disk 58, by way of which the control slide 34 is calibratablein its position is disposed above the gear wheel 50.

[0046]FIG. 5 shows the disposition of a rack 58 on the valve mechanismthat meshes with the gear wheel 50. The rack 58 is displaceable in itslongitudinal direction and with its teeth 56 meshes with the teeth 54 ofthe gear wheel 50.

[0047]FIG. 6, in a sectional view taken along the line C-C of FIG. 5,shows the engagement of the securing disk 58, via two respective ribs60, with the corresponding grooves 62 of the control slide 34.

[0048]FIG. 7, in a sectional view taken along the line D-D of FIG. 5,shows the meshing of the teeth 56 of the rack 52 with the teeth 54 ofthe gear wheel 50.

[0049]FIG. 4, in a detail X of FIG. 3, shows a preferred feature of theinvention, with which a rotationally fixed connection of the securingdisk 58 with the housing of the cylinder head 18 can be established. Therotationally fixed connection is achieved with the aid of the shaping ofbumps 64 on the securing disk 58, which protrude into bores 66 made inthe housing of the cylinder head 18. In this simple and advantageousway, the securing disk 58 is connected in a rotationally fixed andsecure manner to the housing of the cylinder head 18.

[0050] In FIG. 9, the control slide 34 is shown in detail, in the firstexemplary embodiment of the invention. The control slide 34 is embodiedcylindrically, and a thread 46 with a relatively great pitch is machinedinto the outer face of its wall. Two continuous grooves 62 are alsopresent, offset from one another by 180°, in the outer face of its wall,parallel to its center axis.

[0051]FIG. 10 shows the valve mechanism of the invention with itsessential components in a sectional view, for a second exemplaryembodiment of the invention. The fundamental construction of the valvemechanism is analogous to the construction of the valve mechanismdescribed for the first exemplary embodiment. Differences exist incertain details, which will be described below.

[0052]FIG. 11 shows a detail X of FIG. 10. In this view, it can beclearly seen that there is a control slide 34 disposed coaxially to boththe gas exchange valve 12 and the sealing slide 10. The control slide 34(FIG. 14) is provided with a male thread 46, by way of which it isconnected to a corresponding female thread 48 of a gear wheel 50surrounding it. A bore 56 which receives a pin 52 is machined into thecontrol slide 34. The pin 52 protrudes into a housing bore 54 of thecylinder head 18. In this simple and advantageous way, the control slide34 is connected in a rotationally fixed way and securely to the housingof the cylinder head 18.

[0053]FIG. 12 shows the disposition of a rack 58 on the valve mechanismthat meshes with the gear wheel 50. The rack 58 is displaceable in itslongitudinal direction and with its teeth 56 meshes with the teeth 54 ofthe gear wheel 50.

[0054]FIG. 13, in a sectional view taken along the line D-D of FIG. 5,shows the meshing of the teeth 56 of the rack 52 with the teeth 54 ofthe gear wheel 50.

[0055] In FIG. 14, the control slide 34 is shown in detail in the secondexemplary embodiment of the invention. The control slide 34 is embodiedcylindrically, and a thread 46 with a relatively great pitch is machinedonto its outer face. There is also a continuous bore 56 in its wall,parallel to its center axis.

[0056] The valve mechanism shown of the first exemplary embodiment ofthe invention has the following function:

[0057] By means of the valve control unit, which in a preferred featureof the invention is a camshaft 44, the gas exchange valve 12 can eitherbe opened or closed. The gas exchange valve 12 is pressed downward onthe valve shaft 14 via the camshaft 40, as in a conventional valvedrive, the course of motion of the gas exchange valve 12 is thuscontrolled. All known methods that are based on the principle of the cuptappet, tilt lever, drag lever, and the like, can be employed.

[0058] The camshaft 44 operates counter to the restoring force of thevalve spring 16 that is braced on the cylinder head 18 and on the valveplate 20 which moves jointly with the gas exchange valve 12. By rotationof the camshaft 44, the gas exchange valve 12 is pressed downward, andthe sealing seat 28 of the gas exchange valve 12 lifts away from thevalve seat ring 22.

[0059] Via the coupling spring 24, which is under a certain initialtension, the sealing slide 10 is moved in slaved fashion. The couplingspring 24 is braced on the valve plate 20 and on the stop disk 26, whichis connected to the sealing slide 10. As a result, the sealing seat 30of the sealing slide 10 is pressed against the sealing seat 28 of thegas exchange valve 12. Since an annular gap seal exists between thesealing body 38 and the valve seat ring 22, only a very slight airquantity (leakage) can reach the combustion chamber 32.

[0060] The gas exchange valve 12 and thus also the sealing slide 10follow the cam course, until the stop disk 26 strikes the control slide34.

[0061] The control slide 34 is adjustable in the axial direction of thevalve shaft 14 in its outset position relative to the gas exchange valve12. The control slide 34 can be adjusted via a suitable adjusting unit,two preferred embodiments of which are shown in detail in FIGS. 4-9 and11-14. Otherwise, the position of the control slide 34 inside the valvemechanism remains fixed, even if forces are exerted on it from outside.The adjusting units can each be actuatable electrically, hydraulically,or pneumatically.

[0062] As soon as the stop disk 26 strikes the control slide 34, thesealing slide 10 can no longer execute any motion in the openingdirection of the gas exchange valve 12. Since the gas exchange valve 12is moved onward by the camshaft, the sealing seat 28 of the gas exchangevalve 12 lifts away from the sealing seat 30 of the sealing slide 10,and air can penetrate the combustion chamber 32. In the process, thecoupling spring 24 is compressed.

[0063] If the gas exchange valve 12 follows the closing flank of thecamshaft 40, it is pressed in the closing direction by the valve spring16. The sealing seat 28 of the gas exchange valve 12 presses against thesealing seat 30 of the sealing slide 10. The sealing slide 10 is carriedalong, until the sealing seat 28 of the gas exchange valve 12 rests onthe valve seat ring 22, and the gas exchange valve 12 is closed.

[0064] By axial displacement of the position of the control slide 34 viaan adjusting unit, it can be established when the sealing seat 28 of thegas exchange valve 12 will lift from the sealing seat 30 of the sealingslide 10. In this advantageous way, the opening cross section of the gasexchange valve 12 and thus also the quantity of air reaching thecombustion chamber 32 can be regulated.

[0065] The control slide 34 shown in FIG. 9 has a male thread 46 with acertain pitch. The female thread 48 of the gear wheel 50 engages themale thread 46 of the control slide 34.

[0066] In addition, a groove 62 is machined into the control slide 34and is engaged by the strut 60 of the securing disk 58. When thesecuring disk 58 is connected to the housing of the cylinder head 18 ina rotationally fixed manner, a rotary motion of the gear wheel 50 isconverted, via the thread 48, into a displacement motion of the controlslide 34 in the axial direction. The rotary motion of the gear wheel 48is generated with the aid of a longitudinal motion of the rack 52. Thelongitudinal motion of the rack 52 can be effected for instance via ahydraulic or pneumatic cylinder, or via an electric motor, which drivesa gear wheel 50 that meshes with the teeth 56 of the rack 52.

[0067] By means of the invention, it is advantageously possible for theopening cross section of a plurality of gas exchange valves 12 to beregulated with one rack 58.

[0068] To compensate for system tolerances, such as the variations inheight of the control slide 34, the securing disk 58 can be rotated, andat the same time the rack 52 is prevented from moving.

[0069] As a consequence of the rotary motion, because of the friction ofthe female thread 48, the gear wheel 50 will also execute a rotarymotion, specifically until the teeth 54 of the gear wheel 50 contact theteeth 56 of the rack 52. Upon further rotation of the securing disk 58,the control slide 34 executes a reciprocating motion in the axialdirection, since the rack 52 is prevented from moving longitudinally andthus the gear wheel 50 is prevented from rotating. The rotary motion ofthe securing disk 58 is continued until such time as the control slide34 has assumed its intended position.

[0070] Next, a rotationally fixed connection is made between thesecuring disk 58 and the housing of the cylinder head 18. In the exampleshown (FIG. 4), the rotationally fixed connection is achieved with theaid of the shaping of bumps 64 on the securing disk 58, which protrudeinto bores 66 made in the housing of the cylinder head 18.

[0071] The valve mechanism of the second exemplary embodiment of theinvention has the following function:

[0072] The fundamental mode of operation of the valve mechanism isanalogous to the mode of operation of the valve mechanism described forthe first exemplary embodiment. Differences exist in certain details,which are described below.

[0073] The control slide 34 of the adjusting unit shown in FIG. 14 has amale thread 48 with a certain pitch. The male thread 46 of the controlslide 34 is engaged by the female thread 48 of the gear wheel 50. Toachieve the function of the control slide 34, it is necessary to hinderit from making a rotary motion. This can for instance be done, as shownin FIG. 11, with the aid of a pin 52, which is guided in the housingbore 54 of the cylinder head and in the bore 56 of the control slide 34.If the gear wheel 50 executes a rotary motion, then because of thethread 46, the control slide 34 necessarily moves in the axialdirection, since it is prevented by the pin 52 from making a rotarymotion.

[0074] By means of a longitudinal motion of the rack 58, whose teeth 62mesh with the teeth 60 of the gear wheel 50, a rotary motion of the gearwheel 50 and thus a displacement motion of the control slide 34 in theaxial direction can be generated.

[0075] Thus by means of the longitudinal motion of the rack 58, theopening cross section of the gas exchange valve 12 can advantageously beregulated.

[0076] The longitudinal motion of the rack 52 can be effected forinstance via a hydraulic or pneumatic cylinder, or via an electricmotor, which drives a gear wheel 50 that meshes with the teeth 56 of therack 52.

[0077] By means of the invention, it is advantageously possible for theopening cross section of a plurality of gas exchange valves 12 to beregulated with one rack 58. As a result, the embodiment according to theinvention is especially economical.

1. A valve mechanism with a variable valve opening cross section, inwhich the valve mechanism is disposed at an admission opening of aninternal combustion engine and has a gas exchange valve, which is actedon by the force of a valve spring and is displaceable axially back andforth inside a guide by a valve control unit, characterized in that asealing slide (10) is disposed coaxially to the gas exchange valve (12),is acted upon by the force of a coupling spring (24), and isdisplaceable axially back and forth by the valve control unit, and theposition of the sealing slide (10) relative to the gas exchange valve(12) is variable in the axial direction by an adjusting unit, whichessentially comprises a control slide (34), which is adjustable in theaxial direction of the gas exchange valve (12) and is disposed coaxiallyto both the gas exchange valve (12) and the sealing slide (10).
 2. Thevalve mechanism of claim 1, characterized in that the valve control unitis a camshaft (44).
 3. The valve mechanism of claims 1 and 2,characterized in that the gas exchange valve (12) has a rotationallysymmetrical basic construction and comprises a valve shaft (14), onwhose lower end a valve plate (20) is disposed.
 4. The valve mechanismof claim 3, characterized in that the valve plate (20) has a conicalcircumferential face, which forms the sealing seat (28) of the gasexchange valve (12).
 5. The valve mechanism of one of claims 1-4,characterized in that in the closing position of the valve mechanism,the sealing seat (28) of the gas exchange valve (12) directly contactsboth a sealing seat (30) of the sealing slide (10) and a valve seat ring(22) of the cylinder head (18).
 6. The valve mechanism of one of claims1-5, characterized in that the sealing slide (10) comprises a bushlikebearing body (40), which is disposed displaceably axially back and forthinside a guide of the cylinder head (18).
 7. The valve mechanism of oneof claims 1-6, characterized in that the bushlike bearing body (40) ofthe sealing slide (10) forms the guide of the gas exchange valve (12),inside which the gas exchange valve (12) is displaceable axially backand forth.
 8. The valve mechanism of one of claims 1-7, characterized inthat the sealing slide (10), on its lower end, has a cylindrical sealingbody (38), whose outer face forms the sealing seat (30).
 9. The valvemechanism of one of claims 1-8, characterized in that the sealing body(38) is connected to the bearing body (40) via connecting rods (42). 10.The valve mechanism of one of claims 1-9, characterized in that a stopdisk (26) is secured to the bearing body (40) of the sealing slide, nearits upper end.
 11. The valve mechanism of one of claims 1-10,characterized in that the stop disk (26) comprises two parts.
 12. Thevalve mechanism of one of claims 1-11, characterized in that the twoparts of the stop disk (26) are surrounded by a clamping ring (36). 13.The valve mechanism of claim 1, characterized in that the control slide(34) is connected via a male thread (46) to a corresponding femalethread (48) of a gear wheel (50), surrounding it, that is connected to arack (58), by which a longitudinal motion can be executed.
 14. The valvemechanism of claim 13, characterized in that to generate thelongitudinal motion of the rack (58), a hydraulic or pneumatic cylinderis preferably provided.
 15. The valve mechanism of claim 13,characterized in that to generate the longitudinal of the rack (58), anelectric motor, which drives a gear wheel (50) that meshes with theteeth (62) of the rack (58), is preferably provided.
 16. The valvemechanism of claims 1 and 13-15, characterized in that associated withthe control slide (34) is a securing disk (58), by way of which thecontrol slide (34) is adjustable in the axial direction.
 17. The valvemechanism of claim 16, characterized in that at least one strut (60),which is in engagement with a groove (62) of the control slide (34), isdisposed on the securing disk (58).
 18. The valve mechanism of claims 16and 17, characterized in that at least one bump (64), with which thesecuring disk (58) can be connected in rotationally fixed fashion to thehousing of the cylinder head (18) is disposed on the securing disk (58).19. The valve mechanism of claims 1 and 13-15, characterized in that abore (56) is made in the control slide (34) and receives a pin (52),which protrudes into a housing bore (54) of the cylinder head (18).